Optical system comprising an euv mirror and method for operating an optical system

Abstract

An optical system comprising an EUV mirror, wherein the EUV mirror is provided with an optical surface designed for the reflection of EUV radiation. An EUV beam path generated by an EUV radiation source is directed at the optical surface of the EUV mirror, such that the EUV beam path is incident on the EUV mirror at an angle of not more than 12°. The optical surface is covered with a carbon layer, wherein the carbon layer has a thickness of at least 8 nm. The invention also relates to a method for operating an optical system.

What is claimed is: 
     
         1 . An optical system comprising an EUV mirror, wherein the EUV mirror is provided with an optical surface designed for the reflection of EUV radiation, wherein an EUV beam path generated by an EUV radiation source is directed at the optical surface of the EUV mirror, wherein the EUV beam path is incident on the EUV mirror at an angle of not more than 12°, wherein the optical surface is covered with a carbon layer. 
     
     
         2 . The optical system of  claim 1 , wherein the carbon layer has a thickness of at least 8 nm. 
     
     
         3 . The optical system of  claim 1 , wherein the carbon layer is a carbon layer deposited during the operation of the optical system. 
     
     
         4 . The optical system of  claim 1 , wherein the optical surface is formed by a reflection layer having a thickness of between 20 nm and 200 nm. 
     
     
         5 . The optical system of  claim 1 , wherein the optical surface is formed by a reflection layer of ruthenium. 
     
     
         6 . The optical system of  claim 1 , wherein the angle between the EUV beam path and the optical surface is at least 4°. 
     
     
         7 . The optical system of  claim 1 , comprising a first EUV mirror and a second EUV mirror, wherein the difference between the angle at which the EUV beam path is incident on the first EUV mirror and the angle at which the EUV beam path is incident on the second EUV mirror is smaller than 6°. 
     
     
         8 . The optical system of  claim 7 , wherein the first EUV mirror and the second EUV mirror have the same incidence plane. 
     
     
         9 . The optical system of  claim 7 , wherein the first EUV mirror and the second EUV mirror jointly effect a beam deflection of the EUV beam path which is between 24° and 48°. 
     
     
         10 . The optical system of  claim 7 , wherein no further optical element that modifies the direction of the EUV beam path is arranged between the first EUV mirror and the second EUV mirror. 
     
     
         11 . The optical system of  claim 1 , comprising one or more EUV mirrors on which the EUV beam path is incident at an angle of between 60° and 90°. 
     
     
         12 . The optical system of  claim 1 , comprising a vacuum housing, in the interior of which the EUV mirror is arranged. 
     
     
         13 . The optical system of  claim 12 , wherein a vacuum atmosphere without hydrogen purge gas is present in the vacuum housing. 
     
     
         14 . A method for operating an optical system in which an EUV beam path generated by an EUV radiation source is directed at an optical surface of an EUV mirror, wherein the EUV beam path is directed at the EUV mirror at an angle of not more than 12°, wherein the optical surface is covered with a carbon layer. 
     
     
         15 . The method of  claim 14 , wherein the carbon layer has a thickness of at least 8 nm. 
     
     
         16 . The optical system of  claim 1 , wherein the optical surface is formed by a reflection layer having a thickness in a range from 30 nm to 80 nm. 
     
     
         17 . The optical system of  claim 1 , wherein the angle between the EUV beam path and the optical surface is at least 6°. 
     
     
         18 . The optical system of  claim 1 , wherein the angle between the EUV beam path and the optical surface is at least 8°. 
     
     
         19 . The optical system of  claim 7 , wherein the difference between the angle at which the EUV beam path is incident on the first EUV mirror and the angle at which the EUV beam path is incident on the second EUV mirror is smaller than 4°. 
     
     
         20 . The optical system of  claim 1 , wherein the difference between the angle at which the EUV beam path is incident on the first EUV mirror and the angle at which the EUV beam path is incident on the second EUV mirror is smaller than 2°.